Particles, such as dirt and dust particles, can be separated from a fluid flow using a cyclonic separator. Cyclonic separators have been used in vacuum cleaners, for example, to separate dirt and dust from an air flow. Such separators can comprise relatively low efficiency cyclones for separating large particles from an air flow and higher efficiency cyclones for separating finer particles in the air flow. Such cyclonic separators have been arranged in vacuum cleaners in series, with an upstream cyclonic separator being combined with smaller downstream cyclonic separators arranged in parallel with one another. An arrangement of this type is shown and described in U.S. Pat. No. 3,425,192 to Davis.